Effect of carrier material on the thermodynamic properties and recrystallization kinetics of andrographolide-solid dispersion.

Abstract

Objectives: This work investigated the effect of the lipophilic long carbon chain of carrier material on the thermodynamic properties and the recrystallization kinetics of solid dispersion (SD).

Methods: The thermodynamic properties and recrystallization kinetic parameters of amorphous andrographolide (AG)-PEG8000 laurate (SM12)-SD, AG-PEG8000 palmitate (SM16)-SD and AG-PEG8000 behenate (SM22)-SD were determined and calculated by differential scanning calorimetry combining AGV equation and Avrami equation.

Key findings: From AG-SM12-SD to AG-SM22-SD with the increase of the carbon chain length of carrier material, the glass transition temperature, the maximum relaxation enthalpy and the mean relaxation time of SD increased at first and then decreased; the isothermal crystallization rate constants at different temperatures and non-isothermal crystallization rate constants at different heating rates of SD showed a trend of decreasing at first and then increasing.

Conclusions: Increasing the carbon chain length of polyethylene glycol fatty acid ester can improve the space-limiting effect of the carrier material on the AG molecule, but the carbon chain length of carrier was not the longer the better. SM16 had the appropriate spatial scale, which better limited the molecular mobility of AG in SD, so AG-SM16-SD has better thermodynamic stability and recrystallization kinetic stability.